Method and apparatus for supplying and switching power

ABSTRACT

A dimming power supply includes a power source, a transformer, a full bridge rectifier and a control switch.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. patent application Ser.No. 12/641,310 entitled “Method and Apparatus for Supplying andSwitching Power”, and filed on Dec. 17, 2009, which claimed priority toU.S. Pat. No. 7,656,692 entitled “Method and Apparatus for Supplying andSwitching Power”, filed on Oct. 31, 2007. The aforementionedapplications are assigned to an entity common hereto, and the entiretyof the aforementioned applications are incorporated herein by referencefor all purposes.

BACKGROUND

High voltage power supplies are needed for many types of electronicdevices. A low voltage may be converted to the appropriate high voltageby a transformer and associated signal conditioning components to obtainthe desired voltage and current level. Often multiple electroniccomponents and systems are powered by a single power supply. However,some types of loads may need individual current control. Typical powersupplies provide global voltage or current control, but not individualvoltage or current control for each of a number of outputs. A commonsolution is to provide a separate regulated power supply for each loador a subset of loads but not the entire set of loads, increasing thesize and cost by including a transformer and filtering and controlcircuitry for each load or subset of loads.

An exemplary prior art power supply is illustrated in FIG. 1, in which atransformer 2 and full bridge rectifier 4 are used to convert analternating current (AC) input 6 to a full-wave rectified current topower a load 8. The full bridge rectifier 4 comprises four diodes, withtwo input nodes at anode-cathode junctions between diodes. The fullbridge rectifier 4 also comprises two output nodes, one at acathode-cathode junction between diodes to which the load 8 isconnected, and one at an anode-anode junction that is typicallygrounded. As is known, a direct current (DC) signal may also be providedto the load 8 by connecting a capacitor (not shown) between the outputat the cathode-cathode junction of the full-bridge rectifier 4 andground, thereby smoothing the full-wave rectified current to DC.

SUMMARY

An exemplary embodiment of an apparatus for supplying and switchingpower may include a power source, a transformer, a full bridge rectifierand a control switch. The transformer has a first winding and a secondwinding, the first winding being connected to the power source, thesecond winding having a first tap and a second tap, with the first tapbeing connected to a first load output. The full bridge rectifierincludes four nodes, the first being connected to the second tap of thesecond winding, the second being connected to a second load output, thethird being connected to a reference voltage source. The control switchis connected between a fourth of the four nodes and the referencevoltage source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a prior art power supply.

FIG. 2 is a schematic of an exemplary apparatus for supplying andswitching power.

FIG. 3 a is an exemplary waveform across a control switch in anexemplary apparatus for supplying and switching power.

FIG. 3 b is an exemplary waveform across a load in an exemplaryapparatus for supplying and switching power.

FIG. 4 is a schematic of another exemplary apparatus for supplying andswitching power, including a current sensor.

FIG. 5 is a schematic of another exemplary apparatus for supplying andswitching power, including a resistor as a current sensor.

FIG. 6 is a schematic of an exemplary apparatus for supplying andswitching power having multiple output stages in parallel, using asingle transformer.

FIG. 7 is a schematic of an exemplary apparatus for supplying andswitching power having multiple output stages in parallel, includingmultiple transformers.

FIG. 8 is a schematic of an exemplary apparatus for supplying andswitching power using a 555 timer as an oscillator and a field effecttransistor to switch current through a transformer.

FIG. 9 is a schematic of an exemplary apparatus for supplying andswitching power using a 555 timer as an oscillator and an inverter and anetwork of bipolar junction transistors to switch current through atransformer.

FIG. 10 is a schematic of an exemplary apparatus for supplying andswitching power including stacked transistors with biasing resistors forhigh power applications and an optional current sensor resistor.

FIG. 11 is a schematic of an exemplary apparatus for supplying andswitching power including stacked transistors with biasing capacitorsfor high power applications and an optional current sensor resistor.

FIG. 12 is a schematic of an exemplary apparatus for supplying andswitching power including additional stacked transistors with biasingresistors for high power applications and an optional current sensorresistor.

FIG. 13 is a schematic of an exemplary apparatus for supplying andswitching power including stacked diodes for high power applications.

FIG. 14 is a flowchart of an exemplary operation for supplying power.

FIG. 15 is a schematic of an exemplary apparatus for supplying andswitching power with a half-bridge driver on the primary transformerwinding.

FIG. 16 is a schematic of an exemplary apparatus for supplying andswitching power with a full-bridge driver on the primary transformerwinding.

FIG. 17 is a schematic of an exemplary apparatus for supplying andswitching power with a push-pull driver on the primary transformerwinding.

FIG. 18 is a schematic of an exemplary apparatus for supplying andswitching power with an AC line voltage at the input to a transformer.

FIG. 19 is a schematic of an exemplary apparatus for supplying andswitching power with an AC line voltage input.

FIG. 20 is a schematic of an exemplary apparatus for supplying andswitching power with an AC line voltage input, with an electricallyisolated control input.

FIG. 21 is a schematic of an exemplary apparatus for supplying andswitching power with a waveform generator controlling a driver on theprimary transformer winding.

FIG. 22 is a schematic of an exemplary apparatus for supplying andswitching power with a grounded center tap on the primary transformerwinding.

FIG. 23 is a schematic of an exemplary apparatus for supplying andswitching power with a waveform generator controlling a driver on theprimary transformer winding.

FIG. 24 is a schematic of an exemplary apparatus for supplying andswitching power with a three-phase AC power source to the primarytransformer winding.

FIG. 25 is a schematic of an exemplary apparatus for supplying andswitching power with a controller that provides control based at leastin part on an ambient light detector.

FIG. 26 is a schematic of an exemplary apparatus for supplying andswitching power with a controller that provides control based at leastin part on a motion sensor.

FIG. 27 is a schematic of an exemplary apparatus for supplying andswitching power with a controller that provides control based at leastin part on a smart grid control and monitoring system.

DESCRIPTION

The drawings and description, in general, disclose a method andapparatus of supplying and switching power to one or more loads. Thecurrent through the loads may be individually controlled usingrelatively low voltage pulse width modulated control signals. Multipleloads may be powered and individually controlled and/or switched from asingle power source and by one or more transformers and full bridgerectifiers.

Referring now to FIG. 2, an exemplary embodiment of an apparatus forsupplying and switching power to a load 10 will be described. In thisexemplary embodiment, a power source (not shown) provides a waveform 12to the primary winding of a transformer 14. A full bridge rectifier 16made up of four diodes is connected to one tap of the secondary windingof the transformer 14. (Please note that the use of the phrase “fullbridge rectifier” herein does not imply any traditional connection ofthe inputs and outputs of the diode network.) The load 10 is connectedto the full bridge rectifier 16 and to another tap of the secondarywinding of the transformer 14. In this exemplary embodiment, the portionof the circuit including the transformer 14 and full bridge rectifier 16has inductance and capacitance values having an LC time constant suchthat a square wave on the primary winding of the transformer 14substantially produces a sine wave across the load 10; in certaininstances, additional capacitance and capacitors may be included in thecircuit. Because the direction of the current through the secondarywinding of the transformer 14 and the load 10 alternates, it does notmatter whether the load is connected to the upper or lower tap of thesecondary winding of the transformer 14 except for the relative phaseangle difference depending on how the taps are connected.

A switch 20 such as, for example, an n-channel metal oxide semiconductorfield-effect transistor (NMOSFET) or re-channel field effect transistor(FET) or a bipolar transistor or set of transistors is/are connectedbetween the full bridge rectifier 16 and ground 22, with a pulse widthmodulated (PWM) control signal 24 applied to the control input of theswitch 20 to vary the duty cycle of the current through the load 10. Itis, of course, understood that any suitable transistor can be used; forexample, p-channel MOSFETs (PMOSFETs), bipolar junction transistors,insulated gate bipolar transistors, etc. may be used with or in place ofthe NMOSFETs.

Although the full bridge rectifier 16 generates a rectified sine wave 18through the switch 20 as illustrated in FIG. 3 a, a full sine wave 19 asillustrated in FIG. 3 b is produced across the load 10.

The full bridge rectifier 16 has a pair of input nodes 30 and 32 and apair of output nodes 34 and 36. A first diode 40 is connected in thefull bridge rectifier 16 at the anode to output node 34 and at thecathode to input node 30. A second diode 42 is connected at the anode toinput node 30 and at the cathode to output node 36. A third diode 44 isconnected at the anode to output node 34 and at the cathode to inputnode 32. A fourth diode 46 is connected at the anode to input node 32and at the cathode to output node 36. Input node 30 of the full bridgerectifier is connected to one tap of the secondary winding of thetransformer 14, input node 32 of the full bridge rectifier is connectedto one side of the load 10, and the other side of the load 10 isconnected to another tap of the secondary winding of the transformer 14.Output node 34 of the full bridge rectifier 16 is connected to ground22, and output node 36 of the full bridge rectifier 16 is connected toground 22 through the control switch 24. Note that the load 10 isconnected to a node 32 that is traditionally used as an input to thefull bridge rectifier 16 (between an anode and a cathode), and thecontrol switch 20 is connected to a node 36 that is traditionally usedas the output of the full bridge rectifier 16 (between two cathodes).This configuration provides simple and effective low voltage controlover the current through the load 10, placing the load in what istraditionally the input path of a full bridge rectifier and the controlin what is traditionally the output path. This configuration allows anAC signal to be controlled by a DC switch.

Note that the ground 22 may comprise a local ground or an absoluteground, as desired. For the case of a local ground, this may beaccomplished by simply connecting node 34 at the anodes of diodes 40 and44 to the side of the control switch 24 opposite the full bridgerectifier 16.

The transformer 14 used in the apparatus to supply power as describedherein is not limited to any particular type of transformer and maychange the ratio between the input and output voltage levels in anymanner desired. The terms primary and secondary windings are not to beseen as limiting, and are interchangeable. That is, the power source maybe connected to either winding of a transformer 14 as desired, with theload 10 and full bridge rectifier 16 connected to the other winding. Thevoltage or current can be stepped up or stepped down with thetransformer, depending, for example, on the particulars of theapplication.

During operation, the power source generates a square wave across theprimary winding of the transformer 14, inducing an alternating currentacross the secondary winding of the transformer 14. Again, in thisexemplary embodiment, the alternating current through the secondarywinding is substantially a sine wave (rectified by the full bridgerectifier across the control switch 20), although the current may beshaped to have any other desired waveform by controlling the LC or RCtime constants of the circuit or by adding other passive or activecomponents as is known in the art. In addition, a sine wave or any otherdesired waveform could be used instead of the square wave as an input tothe primary side of the transformer. The control switch 20 may be usedto turn the current through the load 10 on and off. For the purposes ofthe following discussion, it will be assumed that the control switch 20is on, allowing current to flow through the load 10. During one phase ofoperation, one tap 50 of the secondary winding of the transformer 14will have a higher potential than the other tap 52, such as a positivevoltage at tap 50 and a negative voltage at tap 52. In this phase ofoperation, current will flow in a loop from ground 22, into the outputnode 34 of the full bridge rectifier 16, diode 40, input node 30, thesecondary winding of the transformer 14, the load 10, input node 32,diode 46, output node 36 and through the control switch 20 to ground 22.During the second phase of operation, tap 52 will be at a higherpotential than tap 50, and current will flow in a loop from ground 22,output node 34, diode 44, input node 32, the load 10, the secondarywinding of the transformer 14, input node 30, diode 42, output node 36and through the control switch 20 to ground 22. Thus, at any given timewhen current is flowing through the load 10, two diodes (e.g., 42 and 44or 40 and 46) in the full bridge rectifier 16 are conducting a current.

If the control switch 20 is turned off by the input signal, (for examplea PWM) control signal 24, the terminating path to ground 22 isdisconnected from the load 10 and current cannot flow through the load10. The control signal 24 may be synchronized with the current waveformthrough the secondary winding of the transformer 14 or may beasynchronous as desired, either maintaining unbroken waves in therectified sine wave or chopping them abruptly based on the requirementsof the load 10. The frequencies of the current waveform through thesecondary winding of the transformer 14 and the PWM control signal 24may also be set to any desired rates based on the requirements of theload 10. For example, the current waveform through the secondary windingof the transformer 14 may be set at 50 kHz and the PWM control signal 24may be set at 1 kHz. The width of the pulses on the PWM control signal24 adjusts the duty cycle of the current through the load 10. If the PWMcontrol signal 24 is on for 900 microseconds and off for 100microseconds of each period, the duty cycle of the current through theload 10 will be 900. Note that the PWM control signal 24 of theexemplary embodiment comprises a square wave or series of pulses, butmay alternatively comprise any waveform desired to vary the duty cycleof the current through the load 10, or may alternatively comprise asimple on-off control signal to turn the load 10 on or off withoutvarying the duty cycle.

The method and apparatus for supplying and switching power as describedherein may be used for either low or high voltage loads as desired,while enabling simple low voltage control. For example, several thousandvolts or higher may be provided to the load 10 by selecting diodes inthe full bridge rectifier 16 and a control switch 20 that can withstandhigh voltages without damage. In this case, the control switch 20 maycomprise a single high voltage NMOS transistor or other type oftransistor, or may comprise a stack of transistors as described in U.S.patent application Ser. No. 11/681,767 entitled “Method and Apparatusfor Supplying Power” of Laurence P. Sadwick et al., filed Mar. 3, 2007,which is incorporated herein by reference for all that it discloses.This enables, for example, a PWM control signal 24 of a low voltage,such as 5 volts or 3.3 volts DC, to control a current at a potential ofseveral thousands of volts through the load 10.

Referring now to FIG. 4, another exemplary embodiment of the apparatusfor supplying power may include a current sensor 60, placed anywheredesired in the current path such as between the control switch 62 andground 64. The current sensor 60 may be used to measure the currentlevel through the load 66. The current sensor 60 may comprise anysuitable device for detecting and quantifying current, such as aresistor, an inductively coupled coil, an analog to digital (A/D)converter, etc. For example, the current sensor may comprise a resistor70 as illustrated in FIG. 5, placed between the control switch 72 andground 74. In this embodiment, the current may be detected andquantified by measuring the voltage drop between a node 76 above theresistor 70 and ground 74, using any suitable device such as an A/Dconverter, RMS converter, a filter or set of filters, and/or amplifier.

Referring now to FIG. 6, multiple loads (e.g., 80 and 82) may be poweredby a single transformer 84 and power source (not shown). In thisexemplary embodiment, n loads 80 and 82 are connected to one tap of thesecondary winding of the transformer 84, and n full bridge rectifiers 86and 90 are connected to the other tap of the secondary winding of thetransformer 84 as described above with respect FIG. 2. Note that it isnot necessary that the loads 80 and 82 all be connected to the same tapof the secondary winding of the transformer 84, the load 82 and 84 andfull bridge rectifier 86 and 90 may be interchanged if desired, and mayalso be connected to center taps on the secondary winding of thetransformer 84 if desired to provide different maximum voltage levelsacross the loads 82 and 84. Each load 80 and 82 may be individuallycontrolled by a dedicated control signal 92 and 94, and the currentthrough each load 80 and 82 may be individually monitored by optionaldedicated current sensors 96 and 98 if desired.

In an alternative embodiment for powering n loads as illustrated in FIG.7, each load (e.g., 100 and 102) is provided with a dedicatedtransformer 104 and 106. The transformers 104 and 106 may be identical,or may be individually selected to match the requirements of each load,such as to provide different maximum voltage levels or currents based onthe same input waveform from the power source. Each load 100 and 102 isprovided with a full bridge rectifier 110 and 112 and may beindividually controlled by independent control switches 114 and 116 andPWM control signals 120 and 122. Current through each load may also beindividually monitored by including current sensors (not shown) asdiscussed above.

Referring now to FIG. 8, an exemplary embodiment of an apparatus forsupplying power will be described, including an oscillator forgenerating a square wave on the primary winding of a transformer. Anoscillator such as, for example, a 555 timer 130 or other device is usedto generate an alternating waveform such as a square wave or sine waveat any desired frequency. Any suitable oscillator may be used, such as acrystal oscillator, phase locked loop, Wein bridge, Royer, Hartley, orColpitts oscillator, ring oscillator, logic oscillator, operationalamplifier oscillator, bridge oscillator, etc. A switch such as an NMOStransistor 132 applies the waveform generated by the 555 timer 130 tothe primary winding of a transformer 134. Filter capacitors (not shown)and other components may be added as desired across the primary and/orsecondary winding of the transformer 134 for filtering and resonanttuning to obtain the desired output waveform, but may not be necessaryand should be viewed as optional. One or more loads 136, full bridgerectifiers 140, control switches 142 and current sensors 144 may beconnected to the secondary winding of the transformer 134 as describedabove.

In another exemplary embodiment illustrated in FIG. 9, an oscillator 150may be coupled to the primary winding of a transformer 152 via aninverter and driver pair made up of bipolar junction transistors (BJTs)or other devices. The oscillator 150 drives the input of an invertermade up of a BJT transistor 154 and a pullup resistor 156, controlling apair of BJT transistors 160 and 162 that alternately pull the primarywinding of the transformer 152 between power 164 and ground 166.

As mentioned above, the apparatus for supplying and switching power maybe adapted to higher power and higher voltage applications by stackingtransistors as illustrated in FIG. 10. A transformer 170, full bridgerectifier 172 and load 174 are arranged as described in other exemplaryembodiments above or in other suitable alternative arrangements asdesired. A control switch such as n-channel FET 176 is connected betweenthe full bridge rectifier 172 and ground 180. An optional current sensorsuch as a resistor 182 and current sensor output 184 may be included ifdesired as discussed above. Additional switches such as n-channel FETS186 and 190 may be connected in series with the control switch 176. Thegates of the stacked transistors 176, 186 and 190 may be biased by thenodes in a voltage divider made up of resistors 192, 194 and 196.Alternatively (see FIG. 11), in an alternating current environment, thegates of stacked transistors 200, 202 and 204 may be biased by the nodesin a voltage divider made up of capacitors 206, 208 and 210. Note againthat the illustrated current sensor 212 is purely optional and may beomitted or relocated if desired. The additional stacked transistors(e.g., 176, 186 and 190) divide the voltage dropped between thefull-bridge rectifier 172 and ground 180 across the transistors,enabling higher voltage operation. The apparatus for supplying power andswitching may thus be used, for example, as a high voltage relay capableof handling tens of thousands of volts by dividing the voltage acrossmultiple stacked transistors, while still enabling a low voltage controlsignal to turn on and off the output current and to vary the duty cycle.The transistors may be stacked as deeply as desired, as illustrated inFIG. 12. For example, a stack of 10 transistors (e.g., 220, 222 and 224)may be connected in series, each rated for 1000 volts, in order toprovide a 10,000 volt output. The stack of transistors may be biased bya voltage divider chain made up of resistors (e.g., 226, 228 and 230) orcapacitors as desired.

The apparatus for supplying and switching power may also be adapted tohigher power and higher voltage applications by using diodes rated forhigh power or by stacking diodes as illustrated in FIG. 13, or by acombination of the two techniques. For example, each leg of the fullbridge rectifier 240 may include two or more diodes (e.g., 242, 244).The apparatus for supplying and switching power having high power diodesand/or stacked diodes functions as with other exemplary embodiments(e.g., as in FIG. 2), although the higher potentials are safelytolerated by the high power diodes or by dividing them across multiplediodes in each leg of the full bridge rectifier 240.

Referring now to FIG. 14, an exemplary operation for manufacturing apower supply will be described. An alternating waveform generator isconnected 250 to a first winding of a transformer, and a first loadterminal is connected 252 to a first end of a second winding of thetransformer. A second end of the second winding of the transformer isconnected 254 to a first terminal of a full bridge rectifier. A secondload terminal is connected 256 to a second terminal of the full bridgerectifier. A ground is connected 260 to a third terminal of the fullbridge rectifier, and the fourth terminal of the full bridge rectifieris connected 262 to ground through a control switch. In one exemplaryembodiment, the third terminal is a diode anode-anode junction, thefourth terminal is a diode cathode-cathode junction and the first andsecond terminals are diode cathode-anode junctions. The exemplaryoperation may optionally include connecting a current sensor between thecontrol switch and ground.

Note that any desired waveforms may be used across the primary andsecondary windings of the transformer (e.g., 14) and thus across theload (e.g., 10). Similarly, any desired waveform may be used as thecontrol signal to operate a control switch (e.g., 20), such as a pulsewidth modulated signal, a sine, triangle, sawtooth or square wave, or apulse or stepped signal.

The method and apparatus for supplying and switching power describedherein provides a very effective solution for providing individuallycontrollable currents to multiple loads using a single power source andoptionally one or more transformers. A sine wave or any other desiredwaveform may be driven in alternating directions through the loads, withthe waveform shaped by supplying passive or active wave as desired inthe secondary side of the circuit. Either high or low voltage loadcurrents may be controlled using low voltage control signals, both toturn the load on and off and to vary the duty cycle of the currentthrough the load.

Referring now to FIGS. 15-19, a number of exemplary power sources willbe described for use with the method and apparatus for supplying andswitching power. It is to be noted that these embodiments are purelyexemplary and the method and apparatus for supplying and switching poweris not limited to these embodiments. In one embodiment illustrated inFIG. 15, a half-bridge driver is used to drive one tap of the primarywinding of a transformer 270, with the other tap being grounded. Thehalf bridge driver may comprise a pull-up PFET 272 and a pull-down NFET274, and may be controlled, for example, by a signal from an oscillatorplaced on the control inputs 276 and 280 of the pull-up PFET 272 andpull-down NFET 274. As is understood by those skilled in the art, thetype of transistor may be adjusted as desired. For example, the pull-upPFET 272 may be replaced by a pull-up NFET, in which case the controlinputs of the two transistors would be controlled by complementarysignals.

In another exemplary embodiment illustrated in FIG. 16, the primarywinding of a transformer 290 is powered by a full-bridge driver. One tapof the primary winding is driven by a first side having a pull-up NFET292 and a pull down NFET 294, and the other tap of the primary windingis driven by a second side having a pull-up NFET 296 and a pull-downNFET 298. The full-bridge drive may be controlled by signals from anoscillator, with complementary signals applied to the control inputs ofthe pull-up NFET 292 and pull down NFET 294 and an inverted version ofthose complementary signals applied to the control inputs of the pull-upNFET 296 and pull-down NFET 298. As is understood by those skilled inthe art, the type of transistor may be adjusted as desired, with thecontrol inputs being adapted accordingly. The transistors in this andall other embodiments described herein may comprise N or P channelmetal-oxide-semiconductor field-effect transistors (MOSFETS), junctiongate field-effect transistors (JFETS), insulated gate bipolartransistors (IGBTS), NPN and/or PNP bipolar junction transistors (BJTS),Darlington transistors or any other types of transistors or switchesdesired. Note also that the transformers may be rated for high powerapplications as needed or may be stacked to distribute voltagepotentials across multiple components.

-   -   In another exemplary embodiment illustrated in FIG. 17, the        primary winding of a transformer 300 is powered by a push-pull        driver. Power is supplied to the center tap of the primary        winding, with the end taps alternately pulled down through NFETS        302 and 304 under the control of an oscillator. (See FIG. 21)        Alternatively, the center tap may be grounded with the end taps        alternately pulled up through transistors 302 and 304. (See        FIGS. 22, 23) In yet another alternative, a three phase AC        signal from a power grid or other source may be used, with one        phase connected to the center tap and the other two phases        connected to end taps through transistors 302 and 304. (See        FIG. 24) Multiple phases can be accommodated with multiple        embodiments and switches as described herein. The method and        apparatus for supplying and switching power is not limited to        any particular type or configuration of transformer or means of        driving the transformer. The transformer or alternative power        supply may be run at any desired frequency, such as 50 Hertz, 60        Hertz, 400 Hertz, etc. The transformer, if used, may have a        delta configuration, wye configuration, or any other desired        configuration, etc.

The method and apparatus for supplying and switching power describedherein also may be used to switch AC power using a low voltage controlsignal, using a simple and effective circuit to perform a function thatmight otherwise be performed by solid state relays, triacs, thyristors,mosfet switches, etc. Referring now to FIG. 18, the oscillator of theprevious exemplary embodiments may be replaced by connecting the primarywinding of a transformer 310 to an AC signal, such as the 110 volt ACsignal from a power grid. The AC signal may be connected to thetransformer 310 as desired. For example, one tap of the primary windingmay be connected to the hot lead 312 of an AC signal, with the other 314being connected either to the return line of the AC signal or to aground.

The full bridge rectifier 320 and control switch 322 may be used toswitch AC power through a load 324 without the use of a transformer ifdesired, as illustrated in FIG. 19. To facilitate the description ofthis embodiment, the full bridge rectifier will now be described. Asnoted above, the term “full bridge rectifier” does not imply anytraditional connection at the inputs and outputs, and in fact, the fullbridge rectifiers described herein have a nontraditional connection ofthe inputs and outputs. Also note that the diodes of this embodiment andall others may comprise high voltage diodes if desired, and may alsocomprise stacked diodes as in FIG. 13. A first diode 322 is connected atthe anode to node 324 and at the cathode to node 326. A second diode 330is connected at the anode to node 326 and at the cathode to node 332. Athird diode 334 is connected at the anode to node 324 and at the cathodeto node 336. A fourth diode 340 is connected at the anode to node 336and at the cathode to node 332.

In this embodiment, one lead of an alternating current signal, such asthe hot lead 342 of a 110 volt AC signal from a power grid, is connectedto the one input of the load 324. Another lead of an alternating currentsignal, such as the neutral lead 344 of an alternating current signal,is connected to node 326 of the full bridge rectifier 320. A secondinput of the load 324 is connected to node 336 of the full bridgerectifier 320. Nodes 324 and 332 of the full bridge rectifier 320 form areference voltage point or local ground, and are connected to each otherthrough a control switch 322 such as a transistor. During operation,current flows through the load 324 in alternating directions as long asthe control switch 322 conducts and completes the circuit. During onephase of operation, when input 342 is at a positive potential and input344 is at a negative potential, current flows from input 342, throughthe load 324, diode 340, control switch 322 and diode 322 to input 344.During the other phase of operation, when input 344 is at a positivepotential and input 342 is at a negative potential, current flows frominput 344, through diode 330, control switch 322, diode 334 and the load324 to input 342.

In an alternative embodiment, a current sensor may be placed anywheredesired in the circuit. For example, a resistor may be placed betweenthe control switch 322 and node 324, with a comparator or differentialamplifier connected at each end of the resistor to measure the voltagedrop across the resistor, and correspondingly, the current level throughthe circuit.

Note that the load 324, the control switch 322 and the optional currentsensor may each be placed at any desired point of the circuit throughwhich current flows during both phases of operation, that is, in serieswith either input lead 342 or input lead 344 or in series with thereference voltage point between nodes 324 and 332 of the full bridgerectifier 320.

Referring now to FIG. 20, the control signal 352 and control circuitrymay be electrically isolated from the power source (e.g., the AC line354 and 356) in this or any other embodiment by inserting any suitablecomponent such as an optocoupler 350 or optoisolator between the controlcircuitry and the apparatus for supplying and switching power. Forexample, an optocoupler 350 may be used to electrically isolate thecontrol signal 352 from the transistor 362, thereby enabling low voltagecontrol of the circuit while isolating the control circuitry from surgesor spikes that might pass from the AC line 354 and 356, through the fullbridge rectifier 360 and transistor 362. This exemplary embodiment mayemploy any suitable isolation means and is not limited to an optocoupleror optoisolator.

The embodiments disclosed herein and other embodiments may be adaptedfor use in dimming applications, where a voltage and/or current suppliedto the load is adjusted by a controller. The controller may comprise acircuit, device, program, dimming signal or other type of mechanism forcontrolling the switch to adjust, modify, adapt, switch, or reduce thevoltage and/or current to the load. The controller is connected to thecontrol input of the control switch or transistor at the full bridgerectifier input node, as illustrated in the drawings. The controller mayuse any of a number of suitable control schemes to adjust the voltageand/or current to the load, including pulse width modulation (PWM),analog, digital, phase, voltage dimming, etc. The controller may also bebased on a number of suitable platforms, including one of or anycombination of a microprocessor, microcontroller, FPGA, firmware,hardware, software, control, wired, wireless, Internet, web-based,cellular phone, personal digital assistant (PDA), voice control, etc.

The controller may derive power directly along with the rest of thepower supply disclosed herein, or may derive power from an externalsource, such as solar, mechanical, vibration, RF sources, or battery,etc. The controller may be connected to the control switch in either anisolated or non-isolated fashion as illustrated in the drawings, such asin the direct connection of FIG. 19 or the isolated connection of FIG.20 via optocoupler 350. The controller may be used to dim or adjust thevoltage and/or current to the load under manual control via any suitablemanual interface such as dials, knobs, buttons, switches, voice commandsand voice recognition, etc, or under automatic control such as by acomputer or other programmed or sensory input-based stimulus. Forexample, the controller may be adapted to operate using a daylightharvesting control, or based on ambient light detectors (See FIG. 25)and also coupled with other types of sensor such as motion sensors (SeeFIG. 26), RFID, microphones, etc.

A variety of loads may benefit from dimming or adjusted voltage and/orcurrent levels. For example, light sources may be adapted to a widerrange of uses by a dimming power supply. Motors and appliances may becontrolled by supply voltage and/or current adjustment, either bycontinuous level variation such as by changing the on/off ratio or dutycycle of an input voltage and current to provide dimming and controlledbrown-out capability, or by using discrete supply on/off control. Forexample, appliances may be turned off or operated under lower powerduring brown-out conditions, either under local control or underexternal control in a smart grid control and monitoring system. (SeeFIG. 27) The controller may be adapted to adjust the voltage and/orcurrent levels using any of a number of suitable control schemes, forany of a number of different types of loads for a variety of beneficialpurposes.

While illustrative embodiments have been described in detail herein, itis to be understood that the concepts disclosed herein may be otherwisevariously embodied and employed, and that the appended claims areintended to be construed to include such variations, except as limitedby the prior art.

What is claimed is:
 1. A power supply, comprising: a power source; atransformer comprising a first winding and a second winding, said firstwinding being connected to said power source, said second windingcomprising a first tap and a second tap, said first tap being connectedto a first load output; a full bridge rectifier comprising four nodes, afirst of said four nodes being connected to said second tap of saidsecond winding, a second of said four nodes being connected to a secondload output, and a third of said four nodes being connected to areference voltage source; and a control switch connected between afourth of said four nodes and said reference voltage source.
 2. Thepower supply of claim 1, wherein the power source comprises a driverwith the center tap connected to a power input, the first windingcomprising end taps connected to transistors in the driver, wherein thedriver is operable to alternately pull down the end taps.
 3. The powersupply of claim 2, further comprising an waveform generator operable tocontrol the transistors in the driver to alternately pull down the endtaps.
 4. The power supply of claim 2, wherein the driver comprises apush-pull driver.
 5. The power supply of claim 2, wherein the powerinput comprises a direct current input.
 6. The power supply of claim 1,wherein the power source comprises a driver with a center tap connectedto a ground, the first winding comprising end taps connected totransistors in the driver, wherein the driver is operable to alternatelypull up the end taps to a power input.
 7. The power supply of claim 6,further comprising an waveform generator operable to control thetransistors in the driver to alternately pull up the end taps.
 8. Thepower supply of claim 6, wherein the driver comprises a push-pulldriver.
 9. The power supply of claim 6, wherein the power inputcomprises a direct current input.
 10. The power supply of claim 1,wherein the power source comprises a three phase alternating signalconnected to a center tap and to two end taps of the first winding. 11.The power supply of claim 1, further comprising a controller operable toprovide a control signal to operate the control switch, wherein thecontrol signal provided by the controller is a modulated signal.
 12. Thepower supply of claim 11, wherein the controller is operable to derivepower from a source other than the power source and transformer.
 13. Thepower supply of claim 11, wherein the controller is operable to controlthe power supply based at least in part on an ambient light detector.14. The power supply of claim 11, wherein the controller is operable tocontrol the power supply based at least in part on a motion sensor. 15.The power supply of claim 11, wherein the controller is operable toperform a controlled brown-out.
 16. The power supply of claim 15,wherein the controller is operable to perform the controlled brown-outunder external control in a smart grid control and monitoring system.17. The power supply of claim 15, wherein the controller is operable toperform the controlled brown-out under local control.
 18. The powersupply of claim 1, wherein the control switch is controlled by a controlsignal that is less than about 5 volts and wherein a voltage across thefirst and second load outputs is at thousands of volts.
 19. A powersupply, comprising: an alternating current power source; a transformercomprising a first winding and a second winding, said first windingbeing connected to said power source, said second winding comprising afirst tap and a second tap, said first tap being connected to a firstload output; a full bridge rectifier comprising four nodes, a first ofsaid four nodes being connected to said second tap of said secondwinding, a second of said four nodes being connected to a second loadoutput, and a third of said four nodes being connected to a referencevoltage source; and a control switch connected between a fourth of saidfour nodes and said reference voltage source.